The invention is directed to a strainer apparatus, wherein straining slots or straining gaps are formed between preferably profiled strainer bars, which have base regions that are received in receiving cutouts of support elements and are permanently attached to the support elements. Such strainer apparatuses are also referred to as “Bar strainer apparatuses”. These strainer apparatuses can be formed as planar screening plates or as round strainer baskets.
Strainer apparatuses employing this so-called “bar screening construction” are known in the art. For example, EP 0 316 570 describes a strainer basket and a method for producing the same, which has a straining slots extending parallel to its rotational symmetry axis and which includes individual profile bars or profile strainer bars which are inserted into cutouts that were previously machined by milling and are located on support elements implemented as support rings, where they are affixed by welding or brazing. To provide a permanent connection between strainer bar and receiving cutout on the support element, friction welding or compression welding are mentioned as possibilities. Also contemplated as welding processes are electric, laser beam and electron beam welding or autogenous welding. Another soldering method, in particular brazing, was described as a suitable process, with another suitable high-quality soldering process being vacuum soldering which produces a high-quality permanent connection between strainer bars and support elements, but disadvantageously involves a complex manufacturing process. The strainer basket is produced by inserting profile bars as strainer bars in a scaffold made of support elements, in the described case support rings, which are initially attached by spot welding and subsequently permanently welded. The strainer bars are here permanently welded along a contour, i.e., essentially along the edges of the receiving cutouts. It is also mentioned that these strainer bars can be connected with the support elements by using an adhesive.
EP 0 499 154 B1 discloses a strainer basket, which eliminates welding while still enabling a defined attachment of the strainer bars in the support elements. The individual strainer bars and the support elements are connected with a snap connection, so that the strainer bars can be pressed into the support elements perpendicular to the longitudinal dimensions of the support elements. In this embodiment, a suitable match between the profile of the strainer bars and the receiving cutouts in the support element is required in order to securely clamp the profile cross-sections of the strainer bars in the receiving cutouts of the support elements. The support elements are hereby held by a device in parallel arrangement to one another and with a spacing that corresponds to the spacing of the support elements; the strainer bars are then sequentially pressed into the receiving cutouts disposed on all support elements at once. Also envisioned in the manufacture can be a deflection in the opposite direction to slightly enlarge the receiving cutouts, thereby facilitating insertion of the strainer bars. If gaps are formed between the strainer bar and the support element after deflection, then these gaps are sealed with liquid plastic material (Loctite™) to prevent braid formation.
EP 0 808 941 B1 describes a process for producing a strainer apparatus with slotted openings and a strainer apparatus produced with this process. Accordingly, an economically advantageous process for producing such strainer apparatuses having optimal stability and surface properties is to be provided. The profile strainer bars are hereby moved into their corresponding position in the receiving cutout of the support element simply by insertion and are secured in place, where they remain until a bonding agent provides the final rigid attachment. The bonding agent establishes a non-releasable connection at the contact surfaces, similar to that attained by brazing, welding or with an adhesive. With contact welding only, the bonding agent is the melt formed from the components themselves. Advantageously, with this production method, brazing at a temperature of up to 900° C. can be employed. Optionally, higher temperatures can be selected. An adhesive can alternatively also be used as a bonding agent for making the connection, which allows manufacture at relatively low temperatures. For example, a technical two-component adhesive can be used which maintains the clamping forces between strainer bars in the base region and in the receiving cutouts of the support elements.
EP 1 205 227 A1 describes a process for producing strainer baskets as well as strainer baskets produced with this process. The strainer bars are secured in corresponding receiving cutouts of support elements by first sandblasting the corresponding strainer bars at the contact zones with the support elements to roughen the surface, and subsequently joining the strainer bars with the support elements in these sandblasted regions with an adhesive.
All these conventional strainer apparatuses, where the strainer bars are permanently attached in the support elements by way of a material connection, optionally combined with a force-transmitting and form-fitting connection, require either additional treatment of the contact surfaces, or the base profile of the strainer bars and the associated geometry of the receiving cutouts in the support elements must be matched within close tolerances. With welding processes or brazing processes, there may be an additional difficulty with inaccuracies in the relative attachment of strainer bars and receiving cutouts in the support elements caused by the high temperatures used in these processes and the resulting different thermal expansion properties, which can cause an undesirable wide scatter of the straining slot or gaps and a corresponding inaccuracy in the straining slot geometry.